Intercommunicating telephone system.



H. D. GURRIER.

INTERGOMMUNIOATING TELEPHONE SYSTEM.

APPLICATION IILED NOV. 23, 1907.

Patented Sept-13, 1910.

UNITED STATES PATENT caries.

HIEAM D'. CUBRIEB, OF CHICAGO, ILLINOIS, ASBIGNOR 'I'O WESTERN ELECTRIC COMPANY, OF CHICAGO, ILLINOIS, A CORPORATION OF ILLINOIS.

INTEBCOMMUNICATING TELEPHONE SYSTEM.

-Appl1catlon filed November 23, 1807. Serial No. 403,528.

To all whom it may concern:

Be'it known that I, 11mm! D. Gunman, citizen of the United States, residing at Chica 0, in the county of Cook and State of Il1nois, have invented a certain'new and useful Improvement in Intercommunicating Telephone Systems, of which the following a full, clear, concise, and exact description. i

My invention relatesftp an intercommunieating telephone system, and one feature thereof relates more particularly to an intercommunicating systemv in which outside communication is provided over a trunk line terminating in such a system and multipled with two or more stationsthereof.

Y One object of my invention is to provide a system of increased etliciency in transmission. A further object is to dispense with the induction coil and condenser, usually associated with each telephone set, without impairment of service, and at the same time providing an arrangement which will not result in an unpleasant click in the receiver when ringing current is applied to the local circuits.

A further object of my invention is to obtain the foregoing desirable features of local intercommunlcation in a system which also rovides for communication over a trunk ine having an induction coil and condenser individual to the trunk line and common to all the stations of the intercommunicating system that are associated with the trun My invention consists in an arrangement of circuits and apparatus in which the transmitter and receiver of a station are in series with each other, and in which a retardation coil of low resistance and high impedance is in shunt on the receiver. Said circuit arrangement permits an increased flow of direct current through the transmitter, thereb roviding for efficient transmission; and wlii e allowing only a small direct current flow through the receiver, does not appreciably interfere with the flow of currents of telephonic frequency through said receiver.

A further feature of my invention consists in a combination with the above mentioned shunt on a receiver of a ringing circuit in which current is applied through a resistance which is also inshunt on the receiver. Such arrangement provides means for indicating when the telephone set of the station rung is not in use and at the same time avoids a disagreeable click in the receiver.

A further feature of my invention consists in means for cutting said retardation coil out of circuit when the telephone receiver is associated with a trunk line and for cutting said retardation coil in circuit when the telephone receiver is associated with one of the local lines of the system for local communication.

These and other features of m invention may be more readily understoo by reference to the accompanying drawing, which is a diagram ofcircuits and ap aratus which may be employed in embodymg my invention. I

For the sake of clearness, only two stations of the intercommunicating system and one trunk line terminating therein, are shown, it being obvious that as many trunk lines may be employed as may be deemed necessary; and that the stations of the system may be duplicated within the usual limits. I

In order to show the several features of my invention, I have shown the same embodied in an intercommunicating system in which means are provided at two or more stations for maintaining the circuit continuity of a trunk'line leading to said intercommunicating system and multipled with said stations, said means being in addition to and in substitution of the telephone set at said stations. By such arrangement,

means are provided for holding a calling line while the telephone set used in answering the call is being utilized for communicating with another local station. Likewise the system shown in the drawing provides means whereby said call may be transferred to another station without the act of transferrin causing a disconnect signal at the centra oilice. Such a system also rovides means for holding a trunk line w ile the station at which the call is received may communicate with another local station without the central ofiice party hearing the conversation.

Referring to the drawing, each station is provided with local. ke s associated with the local lines of every ot or station, those at station I being designated L, and those at I It.

tacts when the receiver is on its hook.

battery B furnishes the source of ringingstation I] L. Each station is also provided" with an answering key A associated with its own local line. Idach station is further provided with a ringing key It for apglylng ringing current to the line selected y the operation of the local key. At each station is the usual call hell I), the circuit through which is closed at the switch iolacurrent. In addition to said local answering and ringing keys, which provide for local intcrconununication only, each of said stations is provided with a trunk key '1 and a transfer key K, the function and operation of which will hereinafter be more fully referred to. I 7

It will be noted that with the exception of the ringin key It, all the keys at a station are held ocked down when depressed by means of a plate D, and the depression of one key releases any key already locked down. The manipulation of key It, however, has no effect on any other key, and said key is not adapted to be locked down by the plate D.

Each local station of the intercommunieating system, as shown, for exam le, at station I and station II, is equippe with the usual telephone set com rising a transmitter t and a receiver 1'. aid transmitter and receiver are here shown in series with each other when the receiver is off its hook A shunt onthe receiver at each station,- as for example at station I, extends from the switch hook contact 58 at one terminal of the receiver, through the conductor 47, a normally closed contact 541 of the trunk key T, conductor 59, including retardation coil 53 back to point 60 at the other terminal of said receiver. The retardation coil has a low ohmic resistance and hence lar ely eliminates direct current flow throug li the receiver, but the impedance of the retardation coil is such that the flow of telephonic currents throu h the receiver is not appreciably lessened. t will be noted that the circuit of the retardation coil 53 is closed through contact 54 when the key '1 is in its unoperated position, but is open at said contact when said key is depressed. Means are thus provided for cutting said retardation coil out of circuit when the trunk key is operated to connect the telephone set with the trunk line as will be hereinafter described.

Corresponding with each local station is a local line 1, 1, and 2, 2, respectivel connected with a common battery B tlirough the usual retardation coils C.

The manner'in which a subscriber at one station may call up another station is ob-' vious. For example, if the subscriber at station I desires to communicate with sta tion II he will remove his receiver 1' from its switch hook h, and depress key L thus se -m key L, conductors 10, 2, 11, 12, bell b, con- "tact 13 conductors 14-, 15, back to battery B The subscriber at station II will respond by depressing his answerin key A and 'by removing his receiver '1- 'rom its hook. Stations 1. and II are now intelephonic communication, the telephone sets thereof being connected to local line 2, 2, 30 through local key L and answering key A respectively. Bridged across conductors 2, 2, as before stated, is the retardation coil 0 through which current from battery B is supplied for local communication. T e circuit arrangement just described rovides means whereby the calling party 1s informed whether or not the station called I isbusy. At the time the party at station I depressedhis ringing key; R, current was sup lied for ringing the bell b at station II, sai current flowing through resistance 8. One terminal of the receiver 7' is connected through conductor 9, to one side of said resistance, and the other terminal of the re- 5 ceiver is connected to the other side of said resistance through conductor 16 and the closed contact 6 of the key R. The ringing of the hell I) at station IIcauses a buzz in the receiver r, due to the difi'erence in potential across the terminals of resistance 8, this resistance being in series with the bell at station II. The current flowing through resistance 8 is intermittent, owing to the opening and closing of the circuit in the usual'105 .manner in the contact of the bell b. The

buzz. denotes to the party at station I that the telephone at station II is not in use, since if it were, contact 13 would be open the bell b at station II would not ring, an therparty at station I would not hear a buzz in his receiver.

When the telephone receiver 0 is ofi the hook it, contacts 52 and 58 are closed and the retardation coil 53 is in shunt on the receiver, said shunt including the normally closed contact 54 of key T. Therefore with the key L depressed, as above described, current would be applied to station I as follows: from. battery. B, conductor 55, winding 56 of retardation coil C, conductor 57, contact 3 of key L conductor 25, transmitter t, switch hook it, through the shunt of receiver r, extending'from contact 58, through conductor 47, contact 54 of key '1, conductor 59, including retardation coil 53, to the point 60, and from thence through conductor 9, contact 4 of key L conductor 10, through winding 61 of retardation coil.

C, back to battery B,

' the retardation coil is very low, approximately 2 ohms, while the resistance of the receiver is comparatively high, approximately ohms, and hence there is practically no direct current flow through the receiver. .Howevcr, the high impedance of coil 53 prevents saidshunt seriously impairing the flow of telephone currents through the receiver. It will be observed, therefore, that the shunt on the receiver 1' permits a greater flow of current for transmission pur oses than if the current was supplied sole y through the receiver. The above described shunt on the receiver ralso performs a further function which may now be described, said function being to prevent an objectionable click inthe receiver upon the operation of the ringing key R. As above stated, the receiver 1 is connected across the resistance 8 in the battery supplyringing lead in order to produce a tone or buzz in the receiver for indicating to the callin party that the tele hone at the-station calle is not in use. "T e resistance 8 is low in value in order to produce a low tone in the receiver. Therefore when the key R is depressed, a lo w shunt is placed on the receiver r, and if such shunt were to result in a marked decrease in the current flow through the receiver, a.very objectionable click would be produced. In my invention, however, the retardation coil 53, bein in shunt on the receiver at the time the ringing key is operated practically no current is flowing through the receiver 1'. The placing of a second low shunt on the receiver, due to the operation of the ringing key R, does not therefore cause a large current change to take place in the receiver, and consequently no objectionable click occurs.

It will be observed that the arrangement thus far described in detail provides what is commonly designated as an intercommunicating system. I will now describe the circuits and arrangement whereby such a system may be connected to a central office exchange to provide for outside communication, and means permitting transferring of calls and preventin a disconnect signal at the central office during the interval of transfers Conductors 17, 18, constitute a trunk line extending from the central office exchange to the mtercommunicating system. Said trunk line is multipled, as shown, with each station of the intercommunicating system.

A signal bell b is associated with the trunk line in a manner to give a signal at the stations at which it is desired to answer calls received over the trunk line. The hell 6 may be located, for example, at some point where it can be heard from any station.

As hereinbefore stated, each of the stations with which the trunk line is multithe trunk line. In the drawings,

pled is provided witha trunk key '1 and a transfer key K, associated with the trunk line. The trunk key, when depressed, closes a pair of contacts adapted to connect the ltelephone set of that station to the trunk The function of the transfer key K is to maintain the continuity of the direct current si aling circuit established over the trunk line i substitution of the telephone set, thusena ling that station to call up and communicate with any other station without giving a disconnect si al at the central ollice. As shown in the rawing, such continuit of the trunk line is maintained over a bri go of the line extending from conductor 17 to conductor 18 through conductor 19, including the bell I), contact 20 of a differential relay M and conductor 21, said bridge being normally open at contact 20.

The depression of the transfer key K serves to energize one winding of the relay M and thus cause it to close the contact 20 and to maintain the direct current continuity of the trunk line through the bridge.

Associated with each trunk key '1 is a way-down contact 40 which is closed when said key is completely depressed by the o erator, but which is not closed when ti ie key is merely held down in its usual locked pos1t-ion by the lplate D. The stem 8 of the rey T is of suc length that said key may be depressed sufficiently to close the waydown contact 40. When the pressure is removed from said key, the key rises in the usual manner until the collar 1 thereof engages with the underside of the plate D, said plate holding the key locked in this latter position with the trunk line closed but with the way-down contact open. The closing of said way-down contact performs no function unless the relay -M is already ener ized by the prior operation of a transfer ey, in the manner hereinbefore described. When a transfer key at any station has been operated so as to ener ize the relay M, the subsequent operation of a trunk key. in connecting the tele hone set at any of the stations to the trunli line, closes a circuit through the other winding of: the differential relay, which differential windings thus neutralize the magnetizing effect-of each other. The resultant deiinergization of relay M opens contact 20 in the brldge across the battery B is shown as the source of current for the difierential relay M.

It is ap arent that a call over the trunk line may e answered at any station with which the trunk line is multipled, and the answering station may thereafter secretly communicate with any other station without giving a disconnect signal at the central office, or permitting the central oflice party to hear the conversation. Furthermore, the

answering station may theneither renew the conversation with the calling party, or request the called party to answer over the H, conductor 22, contact 23 of key T, conand conductor 18 'traloflice.

ductor 47, switch hoo h, transmitter t,conductor- 25, contact 26 of key T, conductor 27,

of the trunk line to cen- This completes the direct ourof the trunk line and the central cities that the rent circuit continuity establishes conditions at which show, in the usual manner,

\ call has been answered. Station I is now so tion can take place between the arty and the calling that conversaprivate connected to the trunk line branch exchange party, connected t rough the central exchange, the arty at station I controlling the central 0 cc signals in the usual manner, that-is, by means of his switch hook. If the party at station I now wishes to call up any other station of the intercommunieating system for any purpose, as, for example to receive instructions, or to transfer the call, he presses down the transfer key K, which key is then held down by the plate D. By de ressing key K, the key T is'released, and t e beforementioned bridge is placed across the trunk line conductors 17, 18, thus maintaining the continuity of the direct current signaling circuit of that line, and leav-- ing the arty at station I at liberty to use his telep one for callin up any other station of the private branc exchange.

The circuit conditions brought about by depressing transfer kc 'K are as follows: Current flows from atte B, through conductor 30,, winding'31 o relay M, conductors 32, 33, contact 34 of key K, conductor 35, contact 36, conductors 37, 46, back to battery B. cuit causes relay .M to become energized, closing contacts 20, 38, thereof. The relay M is now locked up through the closed contact 38. The closure of contact 20 short circuits the condenser a and. places a bridge across the trunk line permittmg the flow of direct current, as hereinbefore described. The act of depressin key K has released the key T, thereby isconnecting the telephone setv of station I from the trunk line.

is will be seen, therefore, that by operating key K, the party at station I substitutes a bridge of the trunk ,line for the telephone set, said bridge including contact 20 of the relay M. The party at station I- is now free to communicate with any other local that a call is received fore stated, is locked up -.with t e trunk line. The

side calling party.

the party The closure of this'cir-" station in the manner hereinbefore described, and in the meantime a disconnect signal at the centraloifice is not displayed. In depressing the key L to call up station II for example, the key K. at station I is released, opening energizing relayM, since said relay, as betlirough' its own contact 38. Assuming the party at station I has communicated with the part at station II, either may then connect wit the trunk line by depressin the trunk key T at that station, the condltions brought about being the same in either case. Let us assume, however, that the. arty at station I desires to transfer the 0251 to station II. After calling up station II in the above manner, he instructs the party at that station to answer over the trunk line. The party at station II then de resses his trunk key '1, and in so doing re eases his answering ke leavin the te ephone set connected on y arty at station II is now in position to ta k with the out- The circuits established through the connections of station 11' are substantially the same as those hereinbefore traced from the; trunk line throu h station. I and may be readily followe without further description. A

When the arty at station II answers over the trun line by completely depressing the key T, the contact 40 is c osed.

Current then flows from battery B through conductor 30, conductor 41, contact 40, conductors 42, 43, winding 44 of relay M, conductor 32, contact 38 of relay M, conductors 45, 46, back to battery B The op osin currents in windings 44 and 31 of re ay B will each neutralize the magnetizing effect of the other, and hence relay M will bedeenergized. The direct current bridge across the trunk relay M. The circuit continuity of the trunk line is maintained, however, through the telephone set at station II. The contact 40 of key T remains at station II keeps said key com- Upon removal of the finpletely depressed.

said key moves upward a ger from key T suificient distance is held locked down by plate D to maintaln the other contacts of said key in their closed osition. Upon the part at station II anging up his receiver, tie continuity of the circuit of the trunk line is destroyed at the contacts of the switch hook, and the usual disconnect signal is given at the central office exchange.

I claim 1. In a tele hone system, a transmission circuit, a loca circuit including .a receiver and transmitter in series with each other, and means for controlling the flow of current in said receiver, comprising a normal the contact 34, but not dey as v line is now open at contact 20 of closed only so long as to open contact 40, but

shunt around said receiver, a retardation coil in said shunt, a condenser associated with said transmission circuit, and means for simultaneously removing said shunt and placing said condenser in series circuit with said receiver. i

2. In a telephone system, the combination with a ringing circuit including a vibrating contact, of a resistance included in said ringing circuit, a telephone receiver in shunt on sald resistance, and a retardation coil in shunt on said receiver, said retardation coil being of low ohmic resistance and of high impedance value.

3. In an intercommunicating telephone s stem, the combination with a telephone circuit including a receiver and transmitter in series with each other and with a source of current for said circuit, of a circuit for ringing current, a resistance included in the ringing circuit, said resistance being in shunt on the telephone receiver, and a second shunt on said receiver, said second shunt including a retardation coil of low ohmic resistance and 'of high impedance value.

4. In an intercommunicatin telephone system having a trunk line leading to said system and multipled with two or more stations thereof, the combination with an induction coil and condenser individual to the trunk line and common to all of said stations, of a telephone set at each of said stations having the receiver and transmitter in series with each other, means for associating the telephone set with the local circuits of the intereommunicating system and with the trunk line, respectively, a normally closed shunt on said receiver, a retardation coil of low ohmic resistance and of high impedance value included in said shunt, and means for removing said shunt when said telephone receiver is associated with the trunk lme.

5. In an intercommunicatin telephone system having a trunk line leading to said system and 'multipled with two or more stations thereof, the combination with an induction coil and condenser individual to the trunk line and common to all of said stations, of a telephone receiver at'each of said stations, a retardation coil in shunt on said receiver, said retardation coil having a low ohmic resistance and a high impedance value, means for associating said receiver with the local circuits of the intercommunieating system and "with the trunk line, respective y, and means for cutting said retardation coil in circuit when said receiver is associated with one of the local lines of the system and for cutting said retardation coil out of circuit when said receiver is associated with the trunk line.

6. In an intercommunieatin system having a trunk line lea ing to said system and multipled with two or more stations thereof, the combination with an induction coil and condenser individual to the trunk line and common to all of said stations, of a ringing circuit including a vibrating contact, a resistance included in said ringing circuit, a telephone receiver in shunt on said resistance, a retardation coil in shunt on said receiver, said resistance coil having a low ohmic resistance and a high impedance value, means for associating said receiver with the local circuits of the intercommunieating 5 stem and with the trunk line, respective y, and means for cutting said retardation coil in circuit when said receiver is associated with one of the local lines of the system and for cutting said retardation coil out of circuit when said receiver is associated with the trunk line.

In witness whereof I, hereunto subscribe my 7name this 16th day of November A. D., 190 i RALPH G. JOHANSEN, R. W. INGERBOLL.

telephone 

